A
frequent use of streams is to communicate with a file system
to which groups of data (files) can be written and from which files
can be retrieved.

Common Lisp defines a standard interface for dealing with such a file system.
This interface is designed to be simple and general enough to
accommodate the facilities provided by ``typical'' operating system
environments within which Common Lisp is likely to be implemented.
The goal is to make Common Lisp programs that perform only simple operations
on files reasonably portable.

To this end, Common Lisp assumes that files are named, that given a name one
can construct a stream connected to a file of that name, and that the
names can be fit into a certain canonical, implementation-independent
form called a pathname.

Facilities are provided for manipulating pathnames, for creating
streams connected to files, and for manipulating the file system
through pathnames and streams.